Tests of Lorentz violation in muon antineutrino to electron antineutrino oscillations

A recently developed Standard-Model Extension (SME) formalism for neutrino oscillations that includes Lorentz and CPT violation is used to analyze the sidereal time variation of the neutrino event excess measured by the Liquid Scintillator Neutrino Detector (LSND) experiment. The LSND experiment, performed at Los Alamos National Laboratory, observed an excess, consistent with neutrino oscillations, of ${\bar\nu}_e$ in a beam of ${\bar\nu}_\mu$. It is determined that the LSND oscillation signal is consistent with no sidereal variation. However, there are several combinations of SME coefficients that describe the LSND data; both with and without sidereal variations. The scale of Lorentz and CPT violation extracted from the LSND data is of order $10^{-19}$ GeV for the SME coefficients $a_L$ and $E \times c_L$. This solution for Lorentz and CPT violating neutrino oscillations may be tested by other short baseline neutrino oscillation experiments, such as the MiniBooNE experiment.Comment: 10 pages, 10 figures, 2 tables, uses revtex4 replaced with version to be published in Physical Review D, 11 pages, 11 figures, 2 tables, uses revtex

Search for π0→νμνˉμ\pi^0 \to \nu_{\mu}\bar\nu_{\mu} Decay in LSND

We observe a net beam-excess of $8.7 \pm 6.3$ (stat) $\pm 2.4$ (syst) events, above 160 MeV, resulting from the charged-current reaction of $\nu_{\mu}$ and/or $\bar\nu_{\mu}$ on C and H in the LSND detector. No beam related muon background is expected in this energy regime. Within an analysis framework of $\pi^0 \to \nu_{\mu}\bar\nu_{\mu}$, we set a direct upper limit for this branching ratio of $\Gamma(\pi^0 \to \nu_\mu \bar\nu_\mu) / \Gamma(\pi^0 \to all) < 1.6 \times 10^{-6}$ at 90% confidence level.Comment: 4 pages, 4 figure

Evidence for Neutrino Oscillations from Muon Decay at Rest

A search for nu_bar_mu to nu_bar_e oscillations has been conducted at the Los Alamos Meson Physics Facility using nu_bar_mu from mu+ decay at rest. The nu_bar_e are detected via the reaction (nu_bar_e,p) -> (e+,n), correlated with the 2.2 MeV gamma from (n,p) -> (d,gamma). The use of tight cuts to identify e+ events with correlated gamma rays yields 22 events with e+ energy between 36 and 60 MeV and only 4.6 (+/- 0.6) background events. The probability that this excess is due entirely to a statistical fluctuation is 4.1E-08. A chi^2 fit to the entire e+ sample results in a total excess of 51.8 (+18.7) (-16.9) (+/- 8.0) events with e+ energy between 20 and 60 MeV. If attributed to nu_bar_mu -> nu_bar_e oscillations, this corresponds to an oscillation probability (averaged over the experimental energy and spatial acceptance) of 0.0031 (+0.0011) (-0.0010) (+/- 0.0005).Comment: 57 pages, 34 figures, revtex, additional information available at http://nu1.lampf.lanl.gov/~lsnd

Evidence for nu_mu -> nu_e Neutrino Oscillations from LSND

A search for nu_mu -> nu_e oscillations has been conducted with the LSND apparatus at the Los Alamos Meson Physics Facility. Using nu_mu from pi^+ decay in flight, the nu_e appearance is detected via the charged-current reaction C(nu_e,e^-)X. Two independent analyses observe a total of 40 beam-on high-energy electron events (60 < E_e < 200 MeV) consistent with the above signature. This number is significantly above the 21.9 +- 2.1 events expected from the nu_e contamination in the beam and the beam-off background. If interpreted as an oscillation signal, the observed oscillation probability of (2.6 +- 1.0 +- 0.5) x 10^{-3} is consistent with the previously reported nu_mu_bar -> nu_e_bar oscillation evidence from LSND.Comment: 10 pages (LaTeX), 3 figures (PostScript), submitted to Phys.Rev.Lett. Additional information at http://nu1.lampf.lanl.gov/~lsn

The liquid scintillator neutrino detector and LAMPF neutrino source

A search for neutrino oscillations of the type ν̄μ → ν̄c has been conducted at the Los Alamos Meson Physics Facility using ν̄μ from muon decay at rest. Evidence for this transition has been reported previously. This paper discusses in detail the experimental setup, detector operation and neutrino source, including aspects relevant to oscillation searches in the muon decay-at-rest and pion decay in flight channels

Evidence for νˉμ→νˉe\bar\nu_\mu\to\bar\nu_e Oscillations from the LSND Experiment at LAMPF

A search for $\bar\nu_{\mu}\to \bar\nu_{e}$ oscillations has been conducted at the Los Alamos Meson Physics Facility by using $\bar\nu_\mu$ from $\mu^+$ decay at rest. The $\bar\nu_e$ are detected via the reaction $\bar\nu_e\,p \rightarrow e^{+}\,n$, correlated with a $\gamma$ from $np\rightarrow d\gamma$ ($2.2\,{\rm MeV}$). The use of tight cuts to identify $e^+$ events with correlated $\gamma$ rays yields 22 events with $e^+$ energy between 36 and $60\,{\rm MeV}$ and only $4.6 \pm 0.6$ background events. A fit to the $e^+$ events between 20 and $60\,{\rm MeV}$ yields a total excess of $51.8^{+18.7}_{-16.9} \pm 8.0$ events. If attributed to $\bar \nu_\mu \rightarrow \bar \nu_e$ oscillations, this corresponds to an oscillation probability of ($0.31^{+0.11}_{-0.10} \pm 0.05$)\%.Comment: 4 pages, 3 figures, revtex, psfig. additional information available at http://nu1.lampf.lanl.gov/~lsnd